1. Field of the Invention
The present invention relates to a method for stabilizing the viscosity of polyvinyl acetal resins. More particularly, the present invention is directed to a method for stabilizing the viscosity of the polyvinyl butyral resins used as interlayers for laminated safety glass.
2. Description of the Prior Art
Polyvinyl acetal interlayers are well known in the prior art. These materials are used to prepare laminated safety glass which is used in various vehicle and architectural applications. The most common application for the laminated safety glass is the windshields in automobiles.
The polyvinyl acetal interlayers are subjected to elevated temperatures during extrusion, seasoning of printed sheet and fabrication of the sheet into a laminate. The elevated temperatures cause degradation of the polyvinyl acetal which is evidenced by decreased viscosity and development of yellow color. Some decrease in viscosity may also occur upon aging.
A need exists in the art for a method which will provide polyvinyl acetal interlayers with improved viscosity stability.